Here's a modular collection of ventilation duct work. In purchasing this set, you will find a .max file saved out to v2012 with textures as well as a .fbx versions of each component. The dozen parts all share and reuse one Texture and they are meant to be mixed and matched to meet all your ventilation needs.
The Set was created in 3dsMax with the system unit scale set to 1.0 inches. Please take that into account when planning for use in game engines such as Unreal. Textures include Diffuse and Normal mapping. All images were scanline renders directly from max